From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753238Ab0BAIZV (ORCPT ); Mon, 1 Feb 2010 03:25:21 -0500 Received: from casper.infradead.org ([85.118.1.10]:45740 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750737Ab0BAIZS (ORCPT ); Mon, 1 Feb 2010 03:25:18 -0500 Subject: Re: Lock dependency based tree report in perf lock From: Peter Zijlstra To: Frederic Weisbecker Cc: Hitoshi Mitake , Ingo Molnar , Paul Mackerras , Arnaldo Carvalho de Melo , Thomas Gleixner , "Paul E. McKenney" , LKML In-Reply-To: <20100130185736.GC5675@nowhere> References: <20100129231723.GB5052@nowhere> <1264841188.24455.54.camel@laptop> <20100130185736.GC5675@nowhere> Content-Type: text/plain; charset="UTF-8" Date: Mon, 01 Feb 2010 09:25:04 +0100 Message-ID: <1265012704.24455.80.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2010-01-30 at 19:57 +0100, Frederic Weisbecker wrote: > On Sat, Jan 30, 2010 at 09:46:28AM +0100, Peter Zijlstra wrote: > > On Sat, 2010-01-30 at 00:17 +0100, Frederic Weisbecker wrote: > > > > > > > > > Anyway, that's just an idea, not trivial I must admit. > > > > lockdep actually collects all this information, so writing it out isn't > > too hard. > > > > Lockdep collects the theorical dependencies but not the practical > scenarios. > > Say B and C depend on A, you'll get: > > A > / \ > B C > > But nothing can tell you that if A is taken, B and C will always > be taken. You may have different scenarios based on this dependency, > which is not something that lockdep logs, right? Right. But we keep track of the full held lock stack, which is what was requested.